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Texas Instruments LM3551SD
- Part No.:
- LM3551SD
- Manufacturer:
- Texas Instruments
- Category:
- LED Drivers
- Package:
- 14-WFDFN Exposed Pad
- Datasheet:
-
LM3551SD.pdf
- Description:
- IC LED DRIVER RGLTR 1A 14WSON
- Quantity:
- Payment:
- Shipping:
Inventory:2,813
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Product details
Overview
LM3551SD from Texas Instruments is a fixed-frequency, current-mode step-up DC/DC white LED flash driver with two integrated low-side NFETs (FET-T and FET-F), 1.25MHz switching frequency, 2.7–5.5V input range, and up to 1A total drive current for high-power camera flash applications in single-cell Li-Ion systems.
For engineers reviewing the LM3551SD datasheet, LM3551SD pinout, LM3551SD application, or LM3551SD equivalent, key selection considerations include torch/flash mode control via T/F pin, programmable flash timeout via external CFTO, shutdown logic (active-high SD), over-voltage protection (12.4V typ.), and WSON-14 package thermal performance (θJA = 37.3°C/W).
Technical Context
The LM3551SD implements a current-mode PWM boost converter architecture with internal 0.165Ω SW FET, dual independent low-side current paths (FET-T: 0.98Ω, FET-F: 0.36Ω), and precision 1.265V feedback reference. It supports discrete torch (FET-T only) and flash (FET-T + FET-F) current programming using external RT and RF resistors.
Flash timeout protection uses a 1.4µA constant current into CFTO to generate a 1.16V trip threshold; soft-start is controlled by external CSS charging at 11.5µA; OVP engages at 12.4V (typ.) and releases at 10.6V (typ.), enabling pulsed fault recovery without latch-off.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2.7V to 5.5V - supports full Li-Ion battery discharge curve without brownout. |
| Switching Frequency | 1.25MHz (typ.) - enables use of small 4.7µH inductors and low-ESR ceramic capacitors. |
| Total Drive Current | Up to 1A - sum of torch (≤200mA) and flash (≤500mA) path currents, verified per typical application circuits. |
| Feedback Reference | 1.265V ±0.023V - tight regulation enables accurate LED current setting across temperature. |
| OVP Threshold | 12.4V (typ.) - protects output capacitor, inductor, and SW FET during open-LED or FB short faults. |
| Shutdown Current | 2.55µA (typ.) - ultra-low quiescent draw preserves battery life in standby. |
| Thermal Shutdown | 140°C (typ.) - internal protection prevents permanent damage under sustained overload. |
Pinout & Package
LM3551SD is housed in a 14-pin WSON package (4mm × 4mm, non-pullback, exposed die-attach pad) with 37.3°C/W junction-to-ambient thermal resistance. The exposed GND pad must be soldered to PCB ground plane for thermal and electrical integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VIN | Input power supply | Accepts 2.7–5.5V; connects to Li-Ion battery anode; requires ≥10µF low-ESR ceramic input cap. |
| SD | Shutdown control input | Active-high logic: ≥1.2V = shutdown, ≤0.3V = enabled; internal 1.2MΩ pull-up to VIN. |
| T/F | Torch/Flash mode select | Logic low = torch (FET-T only), logic high = flash (FET-T + FET-F); no internal pull. |
| SW | Boost switch node | Drives external inductor; max 20V swing; 0.165Ω RDSON ensures high efficiency at 1A load. |
| FET-T | Torch FET drain | Connects to cathode of torch-path LED; 0.98Ω RDSON limits torch current to ≤200mA. |
| FET-F | Flash FET drain | Connects to cathode of flash-path LED; 0.36Ω RDSON enables flash current up to 500mA. |
| FB | Current-sense feedback | Monitors voltage drop across RT/RF network; regulates LED current to 1.265V reference. |
| VC | Compensation node | Connects RC/CC network to stabilize loop; pole-zero pair cancels output capacitor pole. |
| FTO | Flash timeout timing | Sinks 1.4µA to charge CFTO; trip at 1.16V sets max flash duration (TFTO = CFTO × 1.21). |
| SS | Soft-start control | Sinks 11.5µA to charge CSS; controls ramp rate of internal reference to limit inrush current. |
| GND / AGND | Analog & power ground | AGND ties compensation components to GND via low-impedance trace; DAP must be soldered. |
| OVP | Over-voltage sense | Ground to disable OVP; floating or pulled high enables 12.4V protection threshold. |
| 1,7,DAP | Ground terminals | Three dedicated GND pins plus exposed DAP ensure low-impedance return path and thermal conduction. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent LED current paths | FET-T (torch) and FET-F (flash) enable simultaneous optimization of continuous and pulsed brightness without shared current-limit trade-offs. |
| Programmable flash timeout | External CFTO sets precise flash pulse duration (e.g., 1µF → ~1.2s), preventing LED thermal damage from software timing errors. |
| True load disconnect in shutdown | Both FET-T and FET-F turn off, and FB network is isolated - shutdown current drops to 2.55µA with zero LED leakage. |
| Integrated OVP with auto-recovery | Clamps output at 12.4V and cycles on/off during persistent fault (e.g., open LED), avoiding latch-up and enabling system-level fault detection. |
| 1.25MHz constant-frequency PWM | Fixed switching frequency simplifies EMI filtering and allows predictable noise spectrum placement outside sensitive bands. |
Applications
| Smartphone Camera Flash | Digital Still Camera (DSC) Flash |
|---|---|
Use Scenario: High-intensity illumination for low-light photo capture in compact mobile devices with space-constrained PCB layouts. IC Role / Device Role / Timing Role: LM3551SD acts as the primary flash LED driver, delivering up to 1A peak current in <2s pulses while managing thermal safety and battery load. Use Value: Enables bright, consistent flash output across full Li-Ion voltage range (4.2V → 3.0V) without requiring external current-sense amplifiers or discrete MOSFETs. | Use Scenario: Synchronized flash triggering in consumer-grade digital cameras where burst-mode operation and rapid recharge are critical. IC Role / Device Role / Timing Role: LM3551SD provides independent torch (preview) and flash (capture) modes, with programmable timeout ensuring safe multi-pulse sequences. Use Value: Eliminates need for separate torch/flash drivers; reduces BOM count by integrating dual FETs, OVP, soft-start, and flash timing in one 4mm × 4mm package. |
| PDA Camera Flash | Camcorder Torch Lamp |
Use Scenario: Compact handheld imaging devices requiring reliable flash performance under variable ambient temperatures and aging batteries. IC Role / Device Role / Timing Role: LM3551SD regulates LED current via FB pin with ±0.023V reference tolerance, maintaining consistent luminance despite input voltage sag or temperature drift. Use Value: Tight feedback accuracy (1.265V ±1.8%) ensures repeatable exposure control without firmware calibration - critical for embedded vision systems. | Use Scenario: Continuous illumination mode in portable video recorders where thermal management and battery runtime are prioritized. IC Role / Device Role / Timing Role: LM3551SD operates in torch mode (T/F = low), enabling stable 200mA LED current with minimal heat generation and no flash-related voltage spikes. Use Value: Low RDSON-T (0.98Ω) and true load disconnect in shutdown extend usable battery life beyond 8 hours in torch-only usage profiles. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar white LED flash driver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LM3552SD | EN pin (active-high enable) instead of SD; identical analog circuitry, pinout, and specs. | Requires active-high host control signal; no internal pull-up - suits systems with dedicated enable GPIO. | Select LM3552SD when host MCU drives EN high to activate; LM3551SD preferred when default-off behavior with pull-up is needed. |
| TPS61310DSKR | Single-path 1.5A boost driver; no dual FETs, no flash timeout, no torch/flash mode separation. | Lacks independent torch/flash control and programmable timeout - requires external logic for mode switching. | Choose TPS61310DSKR only for simple single-mode LED drive; LM3551SD remains superior for camera flash with safety-critical timing. |
Compared with LM3552SD, LM3551SD offers built-in default shutdown via internal VIN-referenced pull-up - reducing host GPIO count. Versus TPS61310DSKR, LM3551SD integrates dual current paths and flash timeout, eliminating external timing components and improving system-level reliability.
Availability
LM3551SD is available at Aetrix Electronics and suitable for smartphone camera flash, digital still camera (DSC) flash, and camcorder torch lamp applications requiring stable component supply, long-term lifecycle support, and automotive-qualified traceability.
Supply support for LM3551SD includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and power management ICs, with decades of expertise in high-efficiency DC/DC conversion and LED lighting solutions.
The LM3551SD belongs to TI's white LED flash driver product line, designed specifically for mobile imaging systems requiring precise, safe, and compact high-current LED drive with integrated fault protection and dual-mode operation.
FAQ
What is the maximum continuous LED current supported by the LM3551SD in torch mode?
The LM3551SD supports up to 200mA continuous LED current in torch mode, determined by the RDSON-T (0.98Ω) and external RT resistor. This value is validated in the Electrical Characteristics table and confirmed in Typical Performance Figures 8 and 9, where torch current remains stable across 2.7–5.5V input range with Lumiled and Sharp LEDs.
How does the LM3551SD implement flash timeout protection, and what external component is required?
The LM3551SD implements flash timeout protection by sinking a precise 1.4µA current from the FTO pin into an external capacitor (CFTO). When the voltage across CFTO reaches 1.16V, the internal flash FETs and SW FET disable. For a 1.2-second timeout, a 1µF capacitor is required (TFTO = CFTO × 1.21 µA/V), as specified in Equation 3 of the datasheet.
What is the function of the SD pin on the LM3551SD, and what logic level enables normal operation?
The SD pin on the LM3551SD is an active-high shutdown input. Normal operation (enabled state) occurs when SD is pulled to ≤0.3V; shutdown occurs when SD ≥1.2V. An internal 1.2MΩ pull-up to VIN ensures default shutdown if the pin is left floating, enhancing system safety during power-up sequencing.
Can the LM3551SD drive both torch and flash LEDs simultaneously, and how is current set for each path?
No - the LM3551SD does not drive torch and flash LEDs simultaneously. Torch mode (T/F = low) activates only FET-T; flash mode (T/F = high) activates both FET-T and FET-F. Torch current is set by RT between FB and FET-T; flash current is the sum of currents through RT and RF (between FB and FET-F), per Equations 4 and 5 in the datasheet.
What package type and thermal characteristics apply to the LM3551SD?
The LM3551SD uses a 14-pin WSON package (package number NHL0014B), measuring 4mm × 4mm with an exposed die-attach pad (DAP). Its junction-to-ambient thermal resistance is 37.3°C/W under standard JEDEC conditions, and the DAP must be soldered to a PCB ground plane to achieve rated thermal performance and electrical stability.
LM3551SD Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 14-WFDFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Type:
- DC DC Regulator
- Topology:
- Step-Up (Boost)
- Internal Switch(s):
- Yes
- Number of Outputs:
- 1
- Voltage - Supply (Min):
- 2.7V
- Voltage - Supply (Max):
- 5.5V
- Voltage - Output:
- -
- Current - Output / Channel:
- 1A (Flash)
- Frequency:
- 1.25MHz
- Dimming:
- -
- Applications:
- Camera Flash
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 14-WSON (4x4)
LM3551SD FAQ
1.How can I place an order for LM3551SD through Aetrix?
Please submit a Request for Quotation (RFQ) for LM3551SD on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for LM3551SD reliable?
The price and inventory of LM3551SD are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM3551SD is usually 5 days.
3.What payment methods are accepted for LM3551SD?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM3551SD transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM3551SD?
LM3551SD orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM3551SD order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for LM3551SD?
For technical support, including LM3551SD datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM3551SD requirements.
6.How does Aetrix verify that LM3551SD is sourced from the original manufacturer or authorized distributors?
All LM3551SD products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that LM3551SD meets industry standards.
7.What is the process for return or replacement of LM3551SD?
All LM3551SD units undergo pre-shipment inspection (PSI). If there is an issue with LM3551SD, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The LM3551SD part is unused and in its original packaging.
Return procedure for LM3551SD:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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